The present invention generally relates to apparatuses for growing crystals, and more particularly to the design of the apparatus used for growing a crystal from a solution under an environment in which the opportunity for accessing the apparatus is limited.
Synthesis of novel materials in space provides a new horizon in the field of semiconductor sciences, material sciences and biological sciences. Particularly, the growth of crystals in space is expected to provide a new material characterized by unique property associate with the microgravity environment in which the material was formed.
In designing the experimental apparatuses for such space experiments, one has to take into consideration various factors that characterize the space experiment such as the enormous transport cost of the experimental apparatuses to space and the limited opportunity for accessing the experimental apparatus. When the apparatus is loaded on an unmanned space vehicle such as a satellite, all the operation of the experiment has to be conducted without human intervention. Even when the apparatus is carried by a manned space vehicle such as a space station or space shuttle, the time or resource that the operator or astronaut can spare for the operation of the apparatus is generally limited. On the other hand, the experiments for processing materials generally need a considerable time, and the apparatus has to be operated continuously for a long time.
One important field of such a space experiment is the growth of protein crystals under the microgravity environment. The growth of protein crystals is an important as well as fundamental step for determining the molecular structure and for investigating the relationship between the structure and function of the protein molecules. Based upon the determination of the molecular structure, it is expected to design the proteins having a desired function. This is one of the major goals of protein engineering.
It should be noted that one needs a protein crystal of the size larger than about 0.3 mm.times.0.3 mm.times.0.3 mm for the precise determination of the molecular structure by the X-ray diffraction analysis. The growth of such a protein crystal is generally made from a solution. On the ground, such a crystallization process is inevitably accompanied with convection caused in the solution, and the repetition of the same experimental condition for obtaining the same quality of protein crystal is extremely difficult. Further, one has to take into consideration the gravitational sedimentation of the protein crystal in the solution that inevitably causes a compositional inhomogeneity in the crystal.
In view of the foregoing problems, the experiments in space for growing the protein crystals under microgravity environments attracts attention of various researchers, as such a microgravity environment does not cause the convection when growing the protein crystals. Herein, the microgravity environment is defined as the environment wherein the acceleration is generally smaller than about 10.sup.-2 G.
Generally, the growth of protein crystals is achieved by controlling the solubility of a protein solution by crystallizing agents. Such crystallizing agents include inorganic salts such as ammonium sulfate, sodium chloride, sodium phosphate, etc. as well as organic salts such as ethanol, methanol, acetone, methylpenthancliol (MPD), etc., and cause a decrease in the solubility of the protein solution. Conventionally, the growth of protein crystals has been made by various methods, some of which are listed below.
a) BATCH METHOD
Form a mixture of the solution of a protein and a crystallizing agent. Leave the mixture for the crystallization. PA1 Change the concentration of the crystallizing agent by providing a concentration gradient. Achieve an optimum crystal growth at an optimum concentration level. PA1 Separate the protein solution and the solution including crystallizing agent by a semipermeable membrane. Achieve the crystallization by transportation of water or crystallizing agent through the semipermeable membrane. PA1 Provide the protein solution and the solution including crystallizing agent adjacent with each other to achieve the crystallization at an interface therebetween. PA1 Provide the protein solution and the solution including crystallizing agent with a separation. Achieve the crystallization by transportation of water or crystallizing agent vapor that causes the difference in the vapor pressure between the protein solution and the solution including the crystallizing agent.
b) GRADIENT METHOD
c) DIALYSIS METHOD
d) FREE INTERFACE DIFFUSION METHOD
e) VAPOR DIFFUSION METHOD
FIGS. 1 and 2 show apparatuses used conventionally in space vehicles for crystallizing protein crystals, wherein the apparatus of FIG. 1 is used for achieving the crystallization according to the batch method. The apparatus of FIG. 2, on the other hand, achieves the crystallization according to the vapor diffusion method.
Referring to FIG. 1, there is provided a block 21 forming the apparatus body, and a plurality of syringe units 1.sub.1, 1.sub.2, . . . are formed in the block 21. Each syringe unit includes a pair of opposing syringes wherein a protein solution 2 and a solution including crystallizing agent 3 are held therein respectively. Upon actuation of the syringes, the protein solution and the crystallizing agent are sent to a crystallizing chamber 4 formed between the opposing syringes, and the protein crystals crystallize in the chamber 4.
In the apparatus of FIG. 2, a plastic tube 22 is used for growing the protein crystals. As shown in FIG. 2, the protein solution 2 and the crystallizing agent 3 are held at both ends of the plastic tube, and the communication between these parts is prohibited by valves or pinch cocks 23.sub.1 and 23.sub.2. Upon releasing of the valves, the communication between the protein solution 2 and the crystallizing agent 3 is established. For example, the solution including crystallizing agent 3 absorbs water that has been vaporized from the protein solution 2 that leads to the oversaturation of the protein solution.
In any of these conventional apparatuses, there is a problem in that the entire apparatus including the block 21 or the tube 22 has to be transported into space together with the protein solution and the solution including crystallizing agent that are the object of the experiment. Thereby, the transportation cost inevitably increases. Further, in the apparatus of FIG. 1, the astronaut has to achieve the manipulation of the syringes. Thereby, considerable resource of the astronaut on the mission is wasted. This problem becomes particularly acute when there are a large number of syringe units in the block 21.
In the apparatus of FIG. 2, the actuation of the pinch cocks can be made automatic by providing an actuating mechanism. However, such a mechanism has to be provided in correspondence to each apparatus 22. Thereby, the weight of the apparatus increases inevitably. Further, these conventional apparatuses generally lack the automatic observation mechanism for automatic observation and recording of the process of crystallization. Thus, the astronaut has to spare valuable resources for checking the progress of crystallization periodically.